hydraulic development

[mahesh420]

Dear all,
to achieve performance, we trimmed impellers to lower the head. but after trimming serious droop is observed at shut off. wondering why it is? can any one help me??????

 

[rajm008]

i think you trimmed the impeller too much. each casing will have a max and minimum impeller dia.

 

[mahesh420]

To Raj,
No sir, trimming is well within the limit

 

[Artisi]

As you increase clearance between impeller OD and the cutwater you can see a droop of CV pressure. There are ways around this problem and is dependant on how the OD of the impeller is machined, but if the impeller is already trimmed it's now too late.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Did it droop before?

Can you post any curves?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1gibson]

It is possible that the trim for that particular pump was only to be applied to the vanes, and the impeller shrouds should have been left at the full diameter. Common on low specific speed pumps, high head low flow (where the impeller looks like a pancake.)

 

[LittleInch]

Who trimmed it?. You or the vendor?

You, then it`s your fault.

The vendor? Ask him.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Is the droop at shut-off a problem, it shouldn't be, as running near to or at shut-off is a NO-NO anyway.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)